Claw-pole machines are synchronous machines in which only one magnet-wheel coil is required for electrically supplying all of the exciter poles with the magnetic excitation required for the magnet-gap field. These machines are especially well-suited for higher pole-pair numbers p, because the salient-pole embodiment that is otherwise necessary provides too little space for the salient-pole coils.
Claw-pole synchronous machines are tried-and-true machines for generating currents in the area of low power. The single excitation pole 1 generates a magnetic field in the axial direction 2 that is partitioned onto the claw poles at the circumference of the rotor and, because of the alternatingly-meshing claw poles in the magnet gap, appears as a magnetic field having an alternating polarity (FIG. 1).
It is known from the European patent publication EP 0394528B1 to provide tangentially-acting permanent magnets to prevent magnetic scattering between the claw-pole fingers and the poles of the claw-pole toothed wheel; in a corresponding design, these permanent magnets support the magnet-gap field of the exciter coils. When the electrical excitation is shut off, the permanent-magnet field magnetically short-circuits over the claw-pole toothed wheel, the claw-pole-finger systems and the exciter yoke, that is, despite the excitation by the permanent magnets, the total magnet-gap field is completely settable.
At higher powers, the claw-pole embodiment is problematic, however, because the magnetically axially-acting exciter coil must encompass the entire exciter useful flux and the scatter flux of all p rotor poles of a claw side. Consequently, the cylindrical exciter yoke, which passes axially through the exciter coil, must have a minimum diameter, as stipulated by the reasonable magnetic saturation, that severely narrows the radial space for the exciter coil unless the embodiment is limited to axially-short stators. A consequence of this is high pole numbers, which, at a given rpm, drive the remagnetization frequency up. This causes greater losses, particularly in the iron parts.